1. Field of the Invention                The present invention is related to an image reading apparatus in which an image reading unit integrating a CCD (Charge Coupled Device) and an optical system comprising a reflection mirror, a condensing lens, etc. is installed to reciprocate in a frame body, specifically an image reading apparatus provided with a contact glass sheet on the upper face of the flame frame body and a sheet of manuscript to be read is placed on the contact glass sheet when reading.        
2. Description of the Related Art
Recently, recycling of constituent parts of industrial machines is proceeding in all industrial circles. As to copying machines and scanner, etc., frames, etc. are generally made of plastic material, and the optical system integrated in the image reading unit is fixed by means of screws and the like for allowing it to be adjusted. Therefore, said optical system is easily detachable for recycling or replacement. The contact glass sheet, on which a sheet of manuscript is to be placed, attached onto the frame body and a slit glass sheet for reading manuscript provided adjacent to the contact glass sheet are also fixed to the frame body by means of fixing members for example as shown in Japanese Laid-Open Patent Application No. 2001-142157 for easing replacement or recycling of the glass sheet when the glass sheet are smeared.
For example, FIG. 7 shows a schematic representation of an image reading apparatus of said prior art. In the drawing, a longitudinal scale plate 101a and a vertical scale plate 101b of scale plates 101 are adhered to a contact glass sheet 102 along two sides thereof respectively by means of double-sided adhesive tape 104 or the like, then the contact glass sheet 102 pasted with the scale plates 101 are placed on a frame body 103 while inserting protrusions 111 of the scale plates 101 into holes 103a provided on the frame body 103. Lastly, a cover 105 (an example of fixing member) for covering the edge part of said scale plates 101 is fixed to the frame body 103 to fixate the scale plates 101 and contact glass sheet 102 on the frame body 103.
However, with the composition like this, first the scale plates 101 are adhered to the two sides of the contact glass sheet and then the contact glass sheet pasted with the scale plates is fixed to the frame body by fitting the protrusions 111 formed on the scale plates into the holes 103a formed on the frame body 103, and further the cover must be attached over the scale plates, so assembling man-hour increases, and further as the contact glass sheet 102 contacts directly to the frame body 103 without using adhesive tape, there is a tendency that clearance is created between the contact glass sheet 102 and frame body 103 due to insufficient flatness of the mating surfaces. Therefore, particles of dust tend to intrude from outside by the effect of air stream produced by the travel of the image reading unit accommodated in the frame body.
Further, when detaching the contact glass sheet from the frame body, the longitudinal plate 101a and vertical plate 101b of the scale plate 101 must be removed, but it is considerably difficult to remove the thin scale plate adhered to the contact glass sheet by means of double-sided adhesive tape 104.
Particularly, when the rear faces of the scale plates are adhered by means of double-sided adhesive tape all over to the contact glass sheet, if a flat-blade screwdriver-like tool is used to strip the scale plates from the contact glass sheet, it is not only difficult to remove the scale plates because the scale plates are thin, but also the contact glass sheet may be hurt or broken due to strong adhering force of the double-sided adhesive tape, resulting in that recycling becomes impossible.